こちらの記事の内容に沿って，レイトレーシングによるCG描画をC++で実装．
https://zenn.dev/mebiusbox/books/8d9c42883df9f6/viewer/b85221
- theta: the angle of field of view
1分35秒(openMP並列なし)→18秒(threads=8)に短縮
# without openmp
./rayt 95.32s user 0.28s system 99% cpu 1:35.84 total
# omp num_threads=8
./rayt 135.03s user 0.32s system 751% cpu 18.011 total